A conventional method of producing a write magnetic pole of a thin film magnetic head is shown in FIGS. 7-10. FIG. 7 is a sectional view of the thin film magnetic head including an air bearing surface. A symbol 10 stands for a thin film magnetic head substrate composed of AlTiC, and a lower shielding layer 12, a magnetoresistance effect element 14, an upper shielding layer 16, a read/write separation layer 18 and a lower magnetic pole 20 are formed on the substrate 10 in this order.
FIG. 8B is a sectional view of the thin film magnetic head including the air bearing surface wherein an upper magnetic pole 26 is formed on the lower magnetic pole 20. A dotted line “A” indicates a position of the air bearing surface. FIG. 8A is a plan view in which the upper magnetic pole 26 is formed. A part of the upper magnetic pole 26 in the vicinity of the air bearing surface is narrower than other parts so as to make a write width narrow. A write gap layer 24, which is composed of a non-magnetic material, e.g., alumina, is formed between the lower magnetic pole 20 and the upper magnetic pole 26.
After the upper magnetic pole 26 is formed, both sides of a base part of the upper magnetic pole 26 are grooved, by FIB (Focused Ion Beam) trimming, toward the lower magnetic pole 20 as shown in FIGS. 10A and 10B. In FIG. 10A, parts “B” of the lower magnetic pole 20 are grooved by FIB trimming.
The both sides of the upper magnetic pole 26 are FIB-trimmed so as to make the write width narrow to improve a write-in accuracy of a write magnetic pole and so as to suppress a magnetic field leak between the upper magnetic pole 26 and the lower magnetic pole 20. By FIB trimming, the grooves are formed at the sides of the lower magnetic pole 20 and distances between the upper magnetic pole 26 and a residual magnetic material located at the sides of the lower magnetic pole 20 are made longer, so that the magnetic field leak can be suppressed. The magnetic field leak between the upper magnetic pole 26 and the lower magnetic pole 20 affects a recording medium to erase signals recorded therein, so that the write-in accuracy must be lowered. To improve characteristics of the thin film magnetic head, the magnetic field leak between the upper magnetic pole 26 and the lower magnetic pole 20 should be suppressed as much as possible.
However, in the case of employing a high saturation magnetic flux density (HiBs) layer 22 in the write magnetic pole, a magnetic field is easily leaked between the upper magnetic pole 26 and the lower magnetic pole 20. Thus, as shown in FIG. 8B, after the HiBs layer 22 and the gap layer 24 are formed on a surface of the lower magnetic pole 20 and the upper magnetic pole 26 are formed, the HiBs layer 22, which is composed of a magnetic material, is removed by ion milling. FIGS. 10A and 10B show a state in which FIB trimming is executed after the ion milling is executed.
However, if the HiBs layer 22 is removed by ion milling so as to make the lower magnetic pole 20 thinner and make the distances between the upper magnetic pole 26 and the residual magnetic material left at the sides of the lower magnetic pole 20 longer to suppress the magnetic field leak between the upper magnetic pole 26 and the lower magnetic pole 20, the upper magnetic pole 26 is simultaneously ion-milled so that the upper magnetic pole 26 must be thinner and the write-in capacity of the write magnetic pole must be lowered.
To further suppress the magnetic field leak between the upper magnetic pole 26 and the lower magnetic pole 20, increasing an amount of FIB-trimming the lower magnetic pole 10 and widening the grooves have been proposed. However, it takes a long time to FIB-trim wide areas, and positions to be FIB-trimmed must be correctly positioned so that productivity must be remarkably lowered.
The present invention was invented to solve the above described problems, and an object of the present invention is to provide a thin film magnetic head, which is capable of solving the problem of magnetic field leak between an upper magnetic pole and a lower magnetic pole and having a high write-in accuracy, and a suitable production method of the thin film magnetic head.